Fronts admin: uses pushState, adds editable settings to trailblocks

* URLs that specify which trailblocks to render now survive OAuth handshakes, because they use a query string param instead of the hash fragment.

* trailblocks have a 'settings' form to specify a ContentApi query and min/max trail length.

* group the List object properties by 'meta', 'config', and 'state' types.